A common car navigation device determines the position of a subject vehicle using a GPS or sensor values of such as a gyroscope and a vehicle speed pulse of the vehicle. In the GPS, radio waves from a plurality of GPS satellites are received and a difference in arrival speed between the radio waves is used to determine an absolute position. In addition, the values of the gyroscope and the vehicle speed pulse are used to determine a relative position of the vehicle from the movement amount thereof if the radio wave from the GPS cannot be received.
However, for achieving a car navigation device at a lower price, there is a car navigation device that does not use a gyroscope and a vehicle speed pulse but only uses a GPS so as to determine the position. Such car navigation device has a problem of being unable to position the subject vehicle in a place where the GPS signal cannot be received and unable to update a map screen display and guide a route. In a long tunnel, in particular, there is a problem of being unable to perform guidance for a long term and, where there is a branching immediately after a tunnel, unable to perform guidance in the tunnel.
Then, Japanese Laid-Open Patent Publication No. 2003-161622 discloses a method by which in a circumstance where a GPS radio wave is blocked such as in a tunnel, a positioning information service of a mobile phone is used so as to determine the position of a subject vehicle without using a gyroscope and a vehicle speed pulse.